Download CirculatorySystem_TheHeart

Heart Seatwork
The heart rests on the _________ surface of
the diaphragm. It lies___________ to the
vertebral column and __________to the
sternum. The base of the heart points to the
_______ shoulder and the apex points
inferiorly toward the _______hip.
• The heart rests on the superior surface of
the diaphragm. It lies anterior to the
vertebral column and posterior to the
sternum. The base of the heart points to
the right shoulder and the apex points
inferiorly toward the left hip.
The Heart
• double pump (blood enters & leaves twice
in one circuit)
1. Size & Location
a. size—(average adult)
about 5.5” long & 3.5” wide
b. location—mediastinal cavity
1) Between lungs, under sternum
2) Apex: left side; between 5th & 6th ribs
2. coverings—double layered,
serous, membranous pericardium
a. Visceral pericardium (epicardium)
directly against heart
b. Parietal pericardium—on the outside
c. Pericardial cavity—between 2 layers
3. Wall of heart (3 layers)
a. epicardium—outer, serous layer. Thin
b. myocardium—middle, thick layer
– Cardiac muscle
c. Endocardium—inner, epithelium &
connective tissue
– Continuous with inner lining of blood vessels
4. Chambers and vessels
a. 4 chambers or cavities
1) two atria—right and left
a) receive blood from veins
b) thin walls & “earlike” auricles
project out
2) two ventricles—right and left
a) pump blood out into arteries
b) thick walls
3) septum—separates heart into right
and left (divides
atria &
ventricles)
b. vessels—veins enter heart,
arteries leave heart
1) veins—enter atria
a) superior & inferior vena
cava bring blood from
body→right atrium; superior
from upper body
regions; inferior from lower.
b) Coronary sinus—wall of
heart into right atrium
c) Pulmonary veins—enter
left atrium from lungs
2) arteries—leave ventricles
a) pulmonary artery—pumps blood from right
ventricle to lungs
b) aorta—pumps blood from left ventricle to
body
5. Valves of the heart (4)
a. Atrioventricular valves—between
atria & ventricles—function: to
prevent backflow into atria
1) Tricuspid valve—right side
2) Bicuspid valve (mitral valve)—left
side
--both valves are composed of flaps
(cusps) to which the chordae
tendineae attach on the lower
surface to keep the cusps in position
--papillary muscles attach to chordae
tendinae & keep them taut.
b. Semilunar valves—between ventricles
and arteries—function: to prevent
backflow into ventricles
1) Pulmonary semilunar—between right
ventricle & pulmonary artery
2) Aortic semilunar—between left ventricle &
aorta
6. Path of Blood through the
Heart
a. Oxygen poor blood
returns to the right atrium
via the vena cavae and
coronary sinus.
b. The right atrium
contracts, forcing blood
through the tricuspid
valve into the right
ventricle.
c. The right ventricle contracts, closing the
tricuspid valve, and forcing blood
through the pulmonary valve into the
pulmonary trunk and arteries.
d. The pulmonary arteries carry blood to
the lungs where it gets rid of carbon
dioxide and picks up a new supply of
oxygen.
e. Freshly oxygenated blood is returned to
the left atrium of the heart through the
pulmonary veins.
f.
The left atrium contracts, forcing blood
through the left bicuspid valve into the
left ventricle.
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g. The left ventricle contracts, closing the
bicuspid valve and forcing open the
aortic valve as blood enters the aorta for
distribution to the body.
7. Blood supply to heart
a. Main supply—right & left coronary artery
b. Drained by cardiac veins
CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Seatwork
• Name the pathway blood takes through
the heart. (Try it without notes)
• Start with the vena cavae (plural) and end
with the systemic (body) circuit.
• Pick up RQ1: Heart
– Due Friday
8. Fetal Adaptations
a. Foramen ovale—opening in the atrial
septum
a. (fetal adaptation that allows oxygenated
blood to enter the left atrium from the right)
8. Fetal Adaptations
a. Ductus arteriosus: fetal adaptation that
prevents blood that enters the right ventricle
from entering the pulmonary circuit;
protects lungs and lets ventricle become strong
9. Heart actions
a. Cardiac cycle (3 phases)
1) Atrial & ventricular diastole
2) Atrial systole & ventricular diastole
3) Ventricular systole & atrial diastole
Diastole = relaxation
Systole = contraction
--heart sounds: closing of valves—
1st one is closing of AV valves as ventricles
contract (lubb)
2nd one is closing of semilunar valves when
ventricles relax (dubb)
b. Cardiac muscle fibers
1) fibers interconnected, called functional
syncytium; function is to conduct impulses
synchronously
2) two in heart:
(a) atrial syncytium—wall of atrium
(b) ventricular syncytium—walls of
ventricles
(c) two connected at floor of right atrium by
fibers of the cardiac conduction system
c. Cardiac conduction system—coordinates
cardiac cycle
(1) specialized muscle fibers initiate &
distribute impulses
(2) sinoatrial node (S-A node); key
portion. Where heartbeat is initiated
Cardiac conduction system:
S-A node
– (a) location; wall of right atrium near superior
vena cava
– (b) excite themselves without outside
stimulation
– (c) rhythmic
– (d) also called pacemaker
– (e) impulses leave S-A node, travel through
walls
– (f) right and left atria contract simultaneously
– (g) impulses lead into atrioventricular (A-V)
node—impulse can’t travel directly to
ventricles
– (3) A-V node—floor of right atrium
• (a) only pathway between atrial & ventricular
syncytia
• (b) delay as impulses pass into node & out of it
• (c) move from node into A-V bundle (Bundle of His)
– it travels into the ventricular septum and branches into
a left & right branch
• (d) branches give rise to Purkinje fibers which
actually distribute impulses to the ventricular
myocardia
– (4) Purkinje fibers
• (a) muscle fibers in ventricular walls are
arranged in irregular whorls, contract in
twisting motion
• (b) contraction starts at apex & moves upward
Video clip & ECG
What is another name for the visceral
pericardium of the heart?
Answer
The Epicardium
Body fluids conduct electrical
currents
• d. electrocardiogram (ECG)
– (1) records changes in electrical activity of
myocardium during cardiac cycle (body fluids
conduct electrical currents)
– (2) electrodes placed on skin; machine
records activity
• Depolarization & repolarization in fibers
• Forms waves
– (3) waves
• (a) P wave—depolarization of atria
• (b) QRS complex—depolarization of ventricles
• (c) T wave—repolarization of ventricles
Normal ECG (sinus rhythm)
– (4) abnormal recordings
• (a) auricular fibrillation
– i. no distinct P wave
– ii. Atria do not distinctly contract (flutter, 200-400/min)
• (b) delayed conduction
– i. greater time period between P & QRS complex
– ii. From 0.2 up to 0.5 seconds
ECG Interpretation
• Graph paper that the ECG records on is
standardized to run at 25mm/second
• Paper is marked at 1 second intervals on the top
and bottom. The horizontal axis correlates the
length of each electrical event with its duration in
time.
• Each small block (defined by lighter lines) on the
horizontal axis represents 0.04 seconds. Five
small blocks (shown by heavy lines) is a large
block, and represents 0.20 seconds.
??
Examples of Abnormal ECGs:
• http://www.ambulancetechnicianstudy.co.u
k/rhythms.html
• e. regulation of cardiac cycle
– (1) rate increased in response to need
– (2) changes often involve factors which affect
the pacemaker
– (3) cardiac center in medulla maintains a
balance between parasympathetic and
sympathetic impulses reaching the heart, or
increases in one or the other. (accelerate or
inhibit the heart rate)
• (a) parasympathetic fibers innervate S-A and A-V
nodes
– i. nerve endings release acetylcholine
– ii. Decreases heart rate (braking action)
– Iii. Less impulses release brake, speeds up rate
• (b) sympathetic fibers innervate nodes by way of
accelerator nerves
– i. endings release norepinephrine
– ii. Increases rate & force of myocardial contractions
• (c) cardiac center receives sensory impulses from
various areas and responds accordingly
– i. pressoreceptors ( aka. baroreceptors) in aortic arch &
carotid sinus are sensitive to changes in blood pressure;
if high, parasympathetic impulses slow rate to drop
pressure
– ii. Also opposite effect
– (4) affect of temperature
• (a) hypothermia—low temperature slows rate
• (b) increased temperature increases rate
– (5) affect of ions
• (a) excess of K+ , hyperkalemia (decrease in rate
and force of contraction)
– Decrease in K+ , hypokalemia (abnormal rhythm,
arrhythmia)
• (b) excessive Ca++ , hypercalcemia (increased rate
or prolonged contraction)
– Low Ca++ , hypocalcemia (depresses heart action,
inhibits heart rate)